Answer the stability review: readers take an index, and the dead branch and field go

AGENTS.md

@@ -138,6 +138,9 @@ live Atlassian APIs; property-generated ADF trees; the CommonMark spec suite aga
 - Nothing recurses unbounded: the guards walk iteratively, and blocks, marks and JSON values — an
   attribute's and a carried node's alike — are all held to 500 levels, so a deep document is a
   `Result` rather than the stack overflow that waits near 2000.
+- A reader takes the text and an index — a sticky regex, `indexOf` — never a fresh slice per
+  character, and a per-character walk hoists what does not vary with the character. The pipeline
+  persona feeds documents nobody typed, so an ordinary megabyte stays milliseconds.
 - No casts: `as`, `as unknown as`, non-null `!`. A boundary owes a type guard validating the
   fields it claims (`isAdfDocument`); past it everything is typed. Make invalid states
   unrepresentable.
@@ -177,8 +180,8 @@ One-line commit messages and PR titles; short PR summaries. No AI-attribution ma
 No wiki markup (§1), no network or filesystem I/O, no name→id resolution (§3), no ADF schema
 validation or exported validator — a refusal that keeps the round-trip is not schema validation,
 so the one a spelled node carrying the same mark type twice earns stays, no shipped CSS (§4), no
-streaming APIs, no performance budget — real documents are kilobytes. A CLI is a later goal
-(`todo.md`), not a non-goal.
+streaming APIs, no performance budget past §11's linear scan — nothing here is tuned, and no
+figure is promised. A CLI is a later goal (`todo.md`), not a non-goal.
 
 ## 15. The working loop